DE102011081345A1 - Method for creating a model - Google Patents

Abstract

Methods for creating a physical model for a real physical system and an arrangement for performing the method are presented. The physical model is determined by model parameters, where known and unknown model parameters are present, and based on measurements on the physical physical system, a data-based system is trained and determined with this data-based model of at least one of the unknown model parameters.

Description

The invention relates to a method for creating a physical model of a real system and to an arrangement for carrying out the method.

State of the art

In the development of technical systems models are used to simulate the behavior of these systems. A mathematical model uses the language of mathematics, for example, to describe a technical or physical system. The process of creating the model is called modeling. Modeling determines model parameters that describe the behavior of the model.

A distinction is made between so-called white box models and black box models. In white box models, it is possible to look at them, that is, they are mathematical equations that describe the behavior and states of the system based on known physical and / or chemical relationships. Based on the equations, the system behavior can also be reconstructed with meaningful intermediate variables.

In contrast, black box models are not graphic. Although these include mathematical equations, they do not describe physics but only the relationship between measured data. Thus, no basic assumptions are included, any course is possible, which can result from measurement data.

Gray Box models are called mixed forms of black and white box models.

So that physical models behave correctly in the simulation, the model parameters must be determined as accurately as possible. Since these can not always be determined metrologically, the parameterization of these non-measurable parameters takes place by an optimization of these parameters, in which measurements on the real system are used as the basis to which the model outputs are adjusted. This means that the parameterization of the physical models takes place via individual measurements on the real system.

In the concrete example of the parameterization of a physical air system, physical drive train model or a physical engine emission model, these measurements are carried out at specific operating points, defined by engine speed and engine load. A limitation of the number of measurements is given by the time and cost of the individual measurements. Therefore only comparatively few measurements are carried out. Based on these few measurements, the physical model is parameterized.

The problem is the behavior of the physical system between the actual measured operating points. Since not all possible combinations of input parameters can be measured, there is always an uncertainty or inaccuracy at points that have not been measured but can be adjusted in the model.

The publication DE 10 2008 043 315 A1 describes a method for operating an internal combustion engine whose operation depends on at least one physical quantity which is calculated taking into account at least one parameter. Furthermore, the physical quantity is determined by means of a data-based model. Training data for the data-based model is calculated from the detected characteristic and the detected physical quantity.

From the publication DE 10 2008 001 081 A1 a method for controlling an internal combustion engine is known. For controlling the internal combustion engine, a map-based manipulated variable is determined, wherein a value of a modified manipulated variable for controlling the internal combustion engine is determined with the aid of a data-based model. This data-based model is determined depending on a real value of a combustion characteristic being measured.

The cited documents thus describe the use of a data-based model for predicting physical quantities of a system. For data-based models, however, it should be noted that they do not know any basic physical structure. In addition, the data volume of data-based models is much greater than that of physical models. For this reason, data-based models are only conditionally suitable for use in an application or optimization process.

Disclosure of the invention

Against this background, a method for creating a model according to claim 1 and an arrangement for carrying out the method according to claim 9 are presented. Embodiments result from the dependent claims and the description.

Thus, a method is presented using a data-based model to to parameterize a physical model. This can be done offline without connection to a motor control or the like. Thus, the physical model, which is also used offline, the reality cover the best possible. This is done not only on a few measured progressions, but in the total range, which can be mapped with the help of a data-based model from comparatively few measurements.

It should be noted that the real system is measured technically and that a data-based model is learned or trained on the basis of these technically determined values. In addition, a physical model is developed in which model parameters can also be measured and / or determined from technical data sheets. These are then known model parameters. This is based on technical considerations regarding the behavior and the structure of the system. Unknown model parameters are then determined or determined on the basis of the data-based model. Depending on the requirement, at least one of the unknown model parameters, a necessary number of unknown model parameters or all unknown model parameters can be determined.

Known model parameters are model parameters that are determined, for example, from measurements on the physical physical system or from other known information about the real physical system, for example through documentation such as data sheets. Unknown model parameters are those that are not determined by measurements or other secure information about the real physical system. This may, for example, be due to the fact that these model parameters can not be determined or measured for technical reasons or for reasons of time or costs.

A data-based model can use a set of measurements to model the real system with all conceivable combinations of input parameters. This data-based model can now be used to apply or optimize the parameters of a physical model. The advantage of the method described is therefore that the parameters of the physical system can also be adapted at locations that were not explicitly measured or could not be measured, but instead are interpolated by the data-based model with high accuracy. This saves time and additional measurements and significantly improves the model quality of the physical model.

In addition, the quality of the measurements carried out can be evaluated by means of the data-based model. Due to the statistical approach of the data-based model, outliers can be easily identified, as they differ significantly from the expected course. Furthermore, a statement about the measurement noise and the reproducibility of the system behavior can be made via the statistical analysis of the measurement data.

In particular, data-based models which also provide information about the model uncertainty are suitable for the method. This can be used to specify a scope of the data-based model. This scope or model uncertainty can be used in the optimization to improve the quality and robustness optimization results. An example of data-based models, which indicate the model uncertainty, are the so-called Bayesian regression methods such as Kriging ( "A statistical approach to some mine valuations and allied problems at the Witwatersrand", DG Krige, 1951 ; "The intrinsic random functions, and their applications", G. Matheron, Adv. Appl. Prob., 5, pp 439-468, 1973 ), Gaussian Process Models ( Gaussian Processes for Machine Learning, Rasmussen and Williams, MIT Press, 2006 ), Sparse Gaussian Processes ( "Sparse Gaussian processes using pseudo-inputs"; E. Snelson and Z Ghahramani, Advances in Neural Information Processing Systems 18, pp 1259-1266, 2006 ) and many others. Another possibility for data-based models with model uncertainty are committees of neural networks ( "Validation of Neural Networks in Automotive Engine Calibration", D. Lowe and K. Zapart, 1997 ).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows in a flow chart a method according to the prior art.

2 shows in a flow chart an embodiment of the presented method.

3 shows a schematic representation of an embodiment of the described arrangement for carrying out the method.

Embodiments of the invention

The invention is schematically illustrated by embodiments in the drawings and will be described below in detail with reference to the drawings.

In 1 In a flow chart, a flow of a method for modeling a physical system according to the prior art is shown. In a first step 10 begins the construction of a physical model. In a next step 12 a parameterization of model parameters takes place from a data sheet 14 or similar documents.

In a subsequent step 16 an estimate of the unknown model parameters is made. In parallel, this takes place in one step 20 a measuring of the real system. With the help of readings is in one step 22 carried out an optimization of the unknown model parameters. Subsequently (block 24 ) are the unknown model parameters determined, but only in places that were actually measured. This results in a good agreement of the physical model with the measurements and possibly less good matches in places that were not measured (Block 26 ).

In 2 In the flowchart, a flow of execution of the presented method of modeling a physical system is illustrated. In a first step 30 begins the construction of a physical model. In a next step 32 a parameterization of model parameters takes place from a data sheet 34 or similar documents. At this point, it is also possible to resort to values of measurements in which the system was measured or measured at certain points or operating points.

In a subsequent step 36 an estimate of the unknown model parameters is made. In this case, it is possible to make use of experiences which provide information about which model parameters are difficult or even impossible to determine, for example by measurement. In parallel, this takes place in one step 38 a measurement of the real system and in a further step 40 learning or training a data-based model. Based on the measured values and the trained data-based model is in one step 42 An optimization of the unknown model parameters is performed using the prediction of the data-based model. Subsequently (block 44 ), the unknown model parameters are determined, even in places that were not measured. The result is a good agreement of the physical model with all imaginable measurements, ie with all possible combinations of input parameters (block 46 ).

In one embodiment of the disclosed method, based on theoretical considerations and based on technical considerations, a physical model of the system is first created. The parameters of this model are partly measurable and can be determined from datasheets. However, various parameters can not be determined and therefore unknown, since a suitable measuring technique does not exist. Another obstacle can be too high costs, if, for example, the use of a computer tomograph is necessary.

This can be achieved by measuring the real system with a specific excitation of the input variables and recording the system responses, ie. H. you drive z. B. with a vehicle different driving maneuvers and records these and the vehicle reactions with suitable measuring devices.

The measurements thus serve, on the one hand, to determine model parameters and, on the other hand, to provide a basis for training a data-based model. It can be provided that certain measurement results are used both for parameter determination and for training the data-based model. Alternatively or additionally, it can be provided that measurement results are used exclusively for parameter determination or for training the data-based model.

According to the explained method, a data-based model is trained on the basis of measurements. This model now allows predictions anywhere in the input room, regardless of whether exactly this combination was measured. This trained data-based model is now the reference for the physical model and the unknown model parameters of the physical model can be determined, for example, by an approximation.

It is thus possible in the application process to make optimizations of model parameters of a physical model at locations that were not previously measured explicitly. The data-based model is used, for example, for interpolation.

The physical models created in this way can be used, for example, for the application and optimization of models, which in turn can be used in functions within the framework of a map model in engine control units.

In 3 is a schematic representation of an arrangement for carrying out the method shown in total with the reference numeral 70 is designated. This arrangement comprises a memory device 72 and a computing unit 74 , In the storage device 72 is a physical model 76 a real physical system stored. There are known 78 and unknown model parameters 80 in front.

In the arithmetic unit 74 becomes a data-based model based on measurements on the real system 82 of the real system, in turn, to determine the unknown model parameters 80 is used. In addition, the data-based model 82 used to be already known model parameters 78 and thus also the quality or validity of measurements on the basis of which these model parameters 78 were determined to check.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008043315 A1 [0009]
• DE 102008001081 A1 [0010]

Cited non-patent literature

• "A statistical approach to some mine valuations and allied problems at the Witwatersrand", DG Krige, 1951 [0018]
• "The intrinsic random functions, and their applications", G. Matheron, Adv. Appl. Prob., 5, pp 439-468, 1973 [0018]
• "Gaussian Processes for Machine Learning", Rasmussen and Williams, MIT Press, 2006 [0018]
• "Sparse Gaussian processes using pseudo-inputs"; E. Snelson and Z Ghahramani, Advances in Neural Information Processing Systems 18, pp 1259-1266, 2006. [0018]
• "Validation of Neural Networks in Automotive Engine Calibration", D. Lowe and K. Zapart, 1997 [0018]

Claims (9)

Method of creating a physical model ( 76 ) for a real physical system, where the physical model ( 76 ) by model parameters ( 78 . 80 ), where known ( 78 ) and unknown model parameters ( 80 ), and based on measurements on the real physical system, a data-based model ( 82 ) and with this data-based model ( 82 ) at least one of the unknown model parameters ( 80 ) is determined. Method according to Claim 1, in which the known model parameters ( 78 ) were determined by measurements. Method according to Claim 1 or 2, in which unknown model parameters ( 80 ) by approximation on the basis of the data-based model ( 82 ). Method according to Claim 1 or 2, in which unknown model parameters ( 80 ) by interpolation on the basis of the data-based model ( 82 ). Method according to one of Claims 1 to 4, in which the data-based model ( 82 ) is created on the basis of Gaussian processes. Method according to Claim 5, in which a scope of validity of the data-based model ( 82 ). Method according to Claim 6, in which the determined validity range is used in an optimization. Method according to one of claims 1 to 7, wherein the measurements carried out with the data-based model ( 82 ) be rated. Arrangement for carrying out a method according to one of Claims 1 to 8, having a memory device ( 72 ) for storing a physical model ( 76 ) for a real system with known ( 78 ) and unknown model parameters ( 80 ) and a computing unit ( 74 ), based on measurements on the real system, a data-based model ( 82 ), which is used to determine the unknown model parameters ( 80 ) is used.

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